linux-kernel - Re: [RFC PATCH 1/2] KVM: x86: Add a framework for supporting MSR-based features

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Message-ID: <c5ede174-9fd7-3303-41b8-a14673d8edca@redhat.com>
Date:   Wed, 14 Feb 2018 17:58:57 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Borislav Petkov <bp@...en8.de>,
        Tom Lendacky <thomas.lendacky@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [RFC PATCH 1/2] KVM: x86: Add a framework for supporting
 MSR-based features

On 14/02/2018 17:44, Borislav Petkov wrote:
> On Thu, Feb 08, 2018 at 04:58:46PM -0600, Tom Lendacky wrote:
>> @@ -2681,11 +2731,15 @@ static int __msr_io(struct kvm_vcpu *vcpu, struct kvm_msrs *msrs,
>>  {
>>  	int i, idx;
>>  
>> -	idx = srcu_read_lock(&vcpu->kvm->srcu);
>> +	if (vcpu)
>> +		idx = srcu_read_lock(&vcpu->kvm->srcu);
>> +
>>  	for (i = 0; i < msrs->nmsrs; ++i)
>>  		if (do_msr(vcpu, entries[i].index, &entries[i].data))
>>  			break;
>> -	srcu_read_unlock(&vcpu->kvm->srcu, idx);
>> +
>> +	if (vcpu)
>> +		srcu_read_unlock(&vcpu->kvm->srcu, idx);
> 
> 
> ./include/linux/srcu.h:175:2: warning: ‘idx’ may be used uninitialized in this function [-Wmaybe-uninitialized]
>   __srcu_read_unlock(sp, idx);
>   ^~~~~~~~~~~~~~~~~~~~~~~~~~~
> arch/x86/kvm/x86.c:2739:9: note: ‘idx’ was declared here
>   int i, idx;
>          ^~~
> 
> I know, silly gcc.
> 

Nice point---even better, just push srcu_read_lock/unlock to msr_io or
even msr_io's callers.

Thanks,

Paolo